This invention relates generally to a device and method to reduce the magnitude of a Lorentz force formed on solenoid-based linear contact plate, and more particularly to a device and method to reduce such magnitude while maintaining arc-extinguish features when the contact plate is opened or otherwise de-energized.
Solenoids are often used to open and close relays, switches and related electrical circuit contacts. Typically, a high-voltage contactor employs the solenoid to move a contact plate into selective connection with a pair of stationary current-carrying terminals to complete an electrical circuit between the terminals. The circuit is open (i.e., incomplete) when the solenoid is de-energized, and closed (i.e., complete) when the solenoid is energized. The presence of high voltage and current in the circuit can cause arcing between the contact plate and the terminals in the time immediately after contact is broken. Such arcing is not desirable, especially in high current modes of operation, as the power created by the arc tends to get absorbed by (or otherwise acts upon) nearby components that may not be electrically hardened.
Attempts to reduce or extinguish the arc have included enclosing the contact plate and terminals inside a chamber filled with a dielectric gas that introduces arc-inhibiting features by absorbing some of the energy during the arc formation. Such a configuration also reduces the packaging and provides some level of environment-independent usage. Despite this, such a solution is not preferred due to the increase in device cost and complexity.
In another attempt, supplemental magnet pairs have been placed on opposing sides of the contact plate and terminals to take advantage of the Lorentz force that acts upon the terminals or other current-carrying members that are exposed to the magnetic field. The inherent Lorentz force can be used in the instant immediately after the circuit is opened at the contact plate to accelerate arc elimination by taking advantage of the arc's polarity to stretch it over a larger region. Such an approach is generally satisfactory for helping to extinguish the arc. Unfortunately, the Lorentz force produced by the supplemental magnets is also imparted onto the nearby contact plate during normal closed-circuit operation. Because this force (which by virtue of the orientation of the magnets relative to the current flowing through the contact plate is generally in a direction that could promote premature separation of the contact plate from the terminals) can interfere with the operation of the solenoid in general and the contact plate in specific, there remain ways in which solenoid operation may be improved.
In yet another attempt, a spring used to close the high-voltage contactor can be designed to have a larger spring rate to keep the contact closed during a high-current (or short circuit fault) situation. Such an enhanced spring force may have a tendency to resist premature contact plate opening from the supplemental magnet Lorentz forces discussed above; unfortunately, the stronger spring will necessitate a higher-force solenoid to open the contact. This in turn requires more energy, such as through a larger coil. Such a solution is not preferred due to the concomitant increase in weight, volume, electrical energy usage and cost.
Automotive lithium-ion batteries are being used to provide partial (in the case of hybrid system) or total (in the case of all-electric system) motive power. Significant levels of one or both voltage and current are needed to provide electrical power to a motor that in turn can provide propulsive power to a set of wheels. The high levels of electrical power employed by such battery systems could, if left uncorrected, lead to significant arcing during relay and related switch operation. In systems that employ some form of magnet-based arc-extinguishing (such as that discussed above), Lorentz forces induced by the magnetic fields are large enough to interfere with the plates and contacts of conventional relay and related switch assemblies by moving them to a different degree (or at a different time) than that for which they were designed. In particular, this downwardly-directed force may overcome the bias established by the induced magnetic force on the solenoid's plunger, which could cause inadvertent open contacts and the very arcing that the supplemental magnets were included to avoid. This untimely contact plate opening may have deleterious effects on the operation of a battery-powered automotive propulsion system.